### Summary

There was an issues when using `safe_constantize` on a string that has
the wrong case.

File `em.rb` defines `EM`.
`"Em".safe_constantize` causes a little confusion with the autoloader.
The autoloader finds file "em.rb",
expecting it to define `Em`, but `Em` is not defined.
The autoloader raises a `LoadError`, which is good,
But `safe_constantize` is defined to return `nil` when a class is not found.

### Before

```
"Em".safe_constantize
LoadError: Unable to autoload constant Em, \
expected rails/activesupport/test/autoloading_fixtures/em.rb to define it
```

### After

```
"Em".safe_constantize
# => nil
```

fetch_multi(*names) now returns its results in the same order
as the `*names` requested, rather than returning cache hits
followed by cache misses.

Generally followed the pattern for https://github.com/rails/rails/pull/32034

* Removes needless CI configs for 2.4
* Targets 2.5 in rubocop
* Updates existing CHANGELOG entries for fewer merge conflicts
* Removes Hash#slice extension as that's inlined on Ruby 2.5.
* Removes the need for send on define_method in MethodCallAssertions.

If the same block is included multiple times, we no longer raise an exception
or overwrite the included block instance variable.

Fixes #14802.

[Mark J. Titorenko + Vlad Bokov]

Fixes #34359

Prior to 5.2.0 (2cad8d71), HashWithIndifferentAccess#to_options acted as
an alias to HashWithIndifferentAccess#symbolize_keys. Now, #to_options
returns an instance of HashWithIndifferentAccess while #symbolize_keys
returns and instance of Hash.

This pr makes it so HashWithIndifferentAccess#to_options acts as an
alias for HashWithIndifferentAccess#symbolize_keys once again.

References #34253.

in favor of `array.flatten.pack("U*")` and `string.scan(/\X/).map(&:codepoints)`, respectively.

In favor of String#is_utf8?.

I think this method was made for internal use only, and its usage was removed here: https://github.com/rails/rails/pull/8261/files#diff-ce956ebe93786930e40f18db1da5fd46L39.

- Adding a Float as a duration to a datetime would result in the Float
  being rounded. Doing something like would have no effect because the
  0.45 seconds would be rounded to 0 second.

  ```ruby
    time = DateTime.parse("2018-1-1")
    time += 0.45.seconds
  ```

  This behavior was intentionally added a very long time ago, the
  reason was because Ruby 1.8 was using `Integer#gcd` in the
  constructor of Rational which didn't accept a float value.

  That's no longer the case and doing `Rational(0.45, 86400)` would
  now perfectly work fine.

- Fixes #34008

Use String methods directly instead.

- I found this weird that the LoggerSilence wasn't using the
  `ActiveSupport` namespace (AFAIK all other classes have it).

  This PR deprecate the use of `LoggerSilence` for
  `ActiveSupport::LoggerSilence` instead.

[Gannon McGibbon + Eric Turner]

* Handle more unsafe String methods

* Fix codeclimate issue

* Revert stylistic change

[Janosch Müller + Rafael Mendonça França]

Fixing code block rendering, indentation, backticks, etc.

Co-authored-by: Nno-itsbackpack <no-itsbackpack@github.com>

The method removes and returns the elements for which the block returns a true value.
If no block is given, an Enumerator is returned instead.

```
numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
odd_numbers = numbers.extract! { |number| number.odd? } # => [1, 3, 5, 7, 9]
numbers # => [0, 2, 4, 6, 8]
```

We always add new entries on the top of changelog file.
This commit moves the entry added in 47018a82 up in order to
preserve the chronology.
Follows up 3e2629eb

* test case for fetch cache miss with skip_nil

* abondon nil cache if skip_nil specified

* ensure not cache key for skip nil

* add document with skip_nil for Store#fetch

* add a new change log entry for #25437

* Use process clock instead of Time.now

This fixes any issues with the system clock changing and also eliminates
2 object allocations per event.

* Add start! and finish! methods to the event object so we can record
more information

* Adds cpu time, idle time, and allocation count for a particular event.
Co-authored-by: NAaron Patterson <aaron.patterson@gmail.com>

Firstly, increment and decrement shouldn't care about the particulars of
key expiry. They should only know that they have to pass that responsibility
on to somewhere else.

Secondly, it moves the key normalization back inside the instrumentation like
it was originally. I think that matches the original design intention or at
the very least it lets users catch haywire key truncation.

Thirdly, it moves the changelog entry to the top of the file, where new entries
go. I couldn't understand what the entry was saying so I tried to rewrite it.

Fixes #32610. Closes #32614.

Lua scripts in redis are *blocking*, meaning that no other client can
execute any commands while the script is running. See
https://redis.io/commands/eval#atomicity-of-scripts.

This results in the following exceptions once the number of keys is
sufficiently large:

    BUSY Redis is busy running a script.
    You can only call SCRIPT KILL or SHUTDOWN NOSAVE.

This commit replaces the lua-based implementation with one that uses
`SCAN` and `DEL` in batches. This doesn't block the server.

The primary limitation of `SCAN`, i.e. potential duplicate keys, is of
no consequence here, because `DEL` ignores keys that do not exist.

Before this change missing timezone data for any of the time zones
defined in `ActiveSupport::Timezone::MAPPING` caused a `comparison of
NilClass with ActiveSupport::TimeZone failed` exception.

Attempting to get a timezone by passing a number/duration to `[]` or
calling `all` directly will try to sort sort the values of `zones_map`.
Those values are initialized by the return value of `create(zonename)`
which returns `nil` if `TZInfo` is unable to find the timezone
information.

In our case the exception was triggered by an outdated tzdata package
which did not include information for the "recently" added time zones.

Before 078421ba `zones_map` only
returned the information that have been loaded into `@lazy_zone_map`
which ignored time zones for which the data could not be loaded, this
change restores the previous behaviour.